The Hox homeobox genes encode proteins that are transcriptional regulators with an established role in embryonic development. HoxA4 (homeobox A4), also known as HOX1D or HOX1, is a 320 amino acid protein that localizes to the nucleus and contains one homeobox DNA-binding domain. Expressed in the embryonic nervous system, HoxA4 functions as a sequence-specific DNA-binding transcription factor that is part of a regulatory mechanism that provides cells with positional identities during development. Via its ability to bind DNA, HoxA4 plays an important role in the regulation of gene expression, as well as morphogenesis and differentiation. The gene encoding HoxA4 maps to human chromosome 7, which houses over 1,000 genes and comprises nearly 5% of the human genome. Defects in some of the genes localized to chromosome 7 have been linked to Osteogenesis imperfecta, Williams-Beuren syndrome, Pendred syndrome, Lissencephaly, Citrullinemia and Shwachman-Diamond syndrome.